LVM Volume Group Dynamic LUN Expansion (DLE) and Contraction (DLC) (September 2009)

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max_pv 16 max_pe 1016 max_lv 255 vg_version 1.0
• Without the –v option:
# vgcfgrestore -l -n vg01
Volume Group Configuration information in "/etc/lvmconf/vg01.conf"
VG Name /dev/vg01
---- Physical volumes : 2 ----
/dev/rdsk/c3t1d0 (Non-bootable)
/dev/rdsk/c2t1d0 (Non-bootable)
Making better use of the alternate bad block pool space
Patches on 11i v1 and v2 have resulted in the bad block directory only being used for entries of pre-
existing bad blocks as modern disk devices can perform their own handling of media errors. If the
bad block directory is empty, vgmodify tries to return the space reserved for the alternate bad block
pool to user data. In some cases the alternate bad block pool on a physical volume is greater than the
extent size. When this is the case, and the max_pe is adequate, vgmodify increases the number of
physical extents for the physical volume. When this happens, the number of free extents and total
number of physical extents on the physical volume increases.
Optimization of max_pv and max_pe values
The valu
es displayed in the –t output are not a complete set of all possible choices, but instead are
the optimal ones. For example, if the output shows the following two adjacent lines:
max_pv(-p) max_pe(-e) Disk size (Mb)
35 2556 10224
39 2300 9200
You can apply a max_pv of 36, 37, or 38 to the volume group, but the highest max_pe for all of
these is the same as for 39 (2300). Similarly, you can use a max_pe between 2557 and 2299, but
the highest max_pv is 39. In reality, with a max_pv of 39, the max_pe can range from the highest
physical extent in use on any physical volume in the volume group to 2300. With a max_pe of 2300,
the max_pv can range from the number of physical volumes currently part of the volume group to 39.
Therefore, –t output shows the optimal values, not the complete list. Or to put it another way the most
sensible set of values to use.
The –o option instructs vgmodify to use the highest optimal max_pv and max_pe values. This option
is most commonly used on volume groups that have not been modified by vgmodify and where you
do not need to change any value. It is asking vgmodify to make best use of the metadata space.
Guidance on choosing the max_pv and max_pe values
When adju
sting sizes of an existing or creating a new volume group, picking max_pv and max_pe
has some side effects on the overall volume group configuration. It is best to provision for growth as
best as possible. In general, the larger the extent size (this is the one parameter vgmodify cannot
alter) the larger the volume group can grow. Use the following guidelines:
• From the table mode (the –t option), you can see how max_pv, max_pe, and disk size can
be tuned for your specific needs or growth plans.
• If you plan to increase the number of physical volumes in the volume group, use the disk size
and max_pv columns from the -t output to determine the max_pv setting. You must review
the Logical Volume Management “Configuring for performance section” in the HP-UX
Administrator's Guide for guidance on the number of volume groups. In general, keep the
number of physical volumes to a minimum to improve performance.
• If you have plans to increase the largest size of disk in the volume group, use the max_pv and
max_pe columns from the –t output to determine the size that best meets your needs.
• Choose a setting from the ‘-t’ output that gives an adequate number of physical volumes of
the largest size required.